Grease preparation



Patented Apr. 21, 1953 GREASE PREPARATION George V. Browning, Schenectady, N. Y., and

Glenn M. Webb, Western Springs, 111., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application December 22, 1950, Serial No. 202,442

19 Claims. 1

This invention relates to improvements in the preparation of greases and in particular it relates to the removal of the liquid component of a grease and the substitution therefor of another liquid. More particularly the invention relates to a method for removing the original liquid component of a grease to obtain the expanded soap structure of the grease substantially free of a liquid component.

The preparation of greases has long been an art rather than a sience due to the lack of fundamental knowledge of the physical and chemical requirements for producing satisfactory greases of desired properties from a variety of oleaginous materials. Frequently it is found that a particular liquid vehicle which would be desirable in a grease cannot be milled or homogenized satisfactorily with a particular soap to form a satisfactory grease or cannot be made by the conventional method of heating and cooling the vehicle-soap mixture. By the process of this invention excellent greases can be prepared from such components. Also it is sometimes found that a manufactured grease satisfactory in grease properties, such as consistency, does not meet specifications such as, for example, a wear test, because of the nature of the oil. The only solution to this problem has been the preparation of a new grease, with the consequent waste of materials employed in the original batch. By the process of this invention, however, it is now possible to utilize the soap from the defective grease in the preparation of an improved grease containing a different liquid vehicle while at the same time recovering the original liquid vehicle for use in any suitable manner. These and many other problems which have confronted those skilled in the art of preparing greases may be solved readily by the process of this invention.

It is an object of the present invention to provide a method of removing the liquid component of a grease. Another object of the invention is to remove this liquid component without substantially altering the expanded soap structure of a lubricating grease. A further object is to obtain, in re-usable form, the expanded soap structure from a lubricant grease substantially free of the liquid component. Still another object is to remove the liquid vehicle from a lubricating grease without substantially altering the expanded soap structure of the lubricating grease and to replace such liquid with another liquid vehicle. Other advantages and objects will become apparent from the following description and claims.

In accordance with the present invention the liquid vehicle of a grease can be removed without substantially modifying the structure of the expanded soap by extracting the original liquid vehicle with a solvent and then removing the solvent at about the critical temperature of the solvent. Evaporation of a solvent from the soap structure of a grease at atmospheric pressure results in the collapse of the soap because of the cohesive forces exerted by the liquid in the extremely narrow passages within the structure. As the liquid is withdrawn by evaporation it pulls the walls of the passages together which results in collapse of the structure. In a preferred embodiment of the present invention the grease is solvent extracted with a liquefied normally gaseous hydrocarbon solvent such as liquefied ethane, propane, etc. then placed in a pressure bomb containing additional liquefied normally gaseous hydrocarbon and heated to about the critical temperature of the hydrocarbon but below the melting point of the soap. At such a temperature substantially all the hydrocarbon in the bomb will have been transformed from a liquid to a gas and is slowly permitted to escape from the bomb. Since the soap structure is not afiected by the removal of the dense gas under pressure because the gas does not exert cohesive forces on the walls of these passages the removal of the solvent in this manner results in the recovery of the expanded soap structure substantially free of liquid. The porous soap structure thus obtained functions somewhat like a sponge and it is then possible to introduce into the sponge-like soap structure any desired liquid vehicle. If the solvent were removed by other means, for example atmospheric evaporation, the structure would be collapsed instead of expanded. Addition of a liquid vehicle to soap in this collapsed condition does not result in a satisfactory lubricant grease. 7

Since the initial extraction is in the liquid phase the conditions at which the extraction takes place should be such that the liquid component being extracted as well as the solvent are in the liquid phase. The extraction is most suitably carried out at a temperature of from about F. to about 200 F. and preferably at about 40 F. to about F. It is to be understood that under superatmospheric pressures higher temperatures can be tolerated.

The present invention is applicable to the modification of solid or semi-solid greases of any type. Thus, the grease may be one comprising essentially a hydrocarbon oil and a soap,

. aeseooi such as an alkali metal, alkaline earth metal, or a heavy metal soap, or mixtures thereof. The soap may be a soap of high molecular weight saturated and/or unsaturated carboxylic acids of at least about carbon atoms, and pref- ,e'rably 16 carbon atoms or more, such as the soaps of lauric acid, stearic acid, hydroxy stearic acid, such as 12-hydroxy stearic acid, palmitic acid, myristic, acid, oleic acid, or mixtures of such fatty acid as occur in coconut fatty acids, animal fats and/or fatty acids, fish oil fatty acids, vegetable oil fatty acids, hydrogenated fatty acids, stearin pitch from the distillation bf hydrogenated fish and fatty acids, etc. The metal soaps of such acids can befor example, the soaps of sodium, potassium, lithium, calcium, barium, strontium, aluminum, lead, zinc, tin, etc., or mixtures thereof. The grease can contain at least about 5% soap and as much as 65% or more soap. The invention, however, is not limited to greases of any particular soap content.

The liquid vehicle of the grease which can be removed in accordance with the present invention can be any liquid lubricant, either natural or'synthe'tic, capable of being used in greaseicompositions. Examples'of such liquid vehicles are petroleum oils, synthetic hydrocarbon lubricating oils, such as for example, those 'obtained'by the polymerization of olefins, or oils in the lubricating oil range obtained in the Fischer-Tropsch process. Other suitable synthetic oleaginous compounds withinthe lubricating oil viscosity range are the aliphatic dicarboxylic acid esters of the type disclosed in US. 2,450,222, such as the esters of sebacic, pimelic, azelaic, alkenyl succinic, alkyl maleic acids, etc. The esters of such acids are preferably the aliphatic esters, particularly the branched chain aliphatic esters, as illustrated by the following specific compounds: di-Z-ethyl-hexyl seb'acate, di-sec-amyl sebacate, "di-2-ethylhexyl alkenylsuccinate, di-2- ethoxyethyl sebacate, di-2-('2-methoxyethyoxy) ethyl sebacate, di2-(2-ethylbutoxy). ethylsebacate, di-2-butoxyethyl azelate, di -2-('2'-b'utoxyethoxy) ethyl'alkenylsuccinate,triethylidene sorbitol, di-z-butoxyethyl alkenylsuccinate, etc. Othersynthetic olea'ginous compounds are the esters of a dihydroxy 'thioether, such as are disclosed in U. S. 2,451,895, silicone polymers, the monohydroxy 1,2 'polyoxypropylene aliphatic monoethers of the type described in U. S. 2,488,644, and the like. In addition to the 'foregoing, the present invention is applicable to greases wherein a viscous'polar compound, such as glycerin, is the liquid vehicle. Another example of a polar vehicle is found in certain silicone oils which are miscible only in polar solvents. While the present invention is particularly applicable to the removal of the liquid vehicle in the grease prepared initially with :a petroleum lubricating oil, the invention is not limited thereto but is applicable to the replacement of any liquid vehicle of a grease with.an-'

of the soap. The solvent employed must have a critical temperature below the melting point of the particular soapand the soap must be'sub-J 4 stantially insoluble in such solvents under the conditions of the process. The solvent employed will be governed to a considerable extent by the nature of the liquid vehicles involved, as Well as the typeof soap present in the grease.

The use of solvents having a -critical temperature below about 200 F., or below the tempera ture at which the water of hydration in the grease will be removed, is necessary in the case of hydrous greases. Solvents having higher critical temperatures cannot be removed without the application of relatively high temperatures which will remove water of hydration required for stabilization of such soap structures. However, in the case of anhydrous greases, a solvent having a higher critical temperature may be used. It is preferred that non-polar solvents be used in the prbcess of this invention because of the high solvent action of polar solvents on the soap at temperatures well below the critical temperature of such solvents. Any solvent, however, in which the liquid vehicle is substantially soluble and in which the'soap is substantially insoluble, which has a'critical'temperature below the melting point of the soap' may be used. The non-polar sol vents useful in this invention are the liquefied normally gaseous hydrocarbons, preferably these hydrocarbons having two and three carbon atoms. Typical examples of such hydrocarbons are ethane, ethylene, propane, propylene, butane, etc. Butane has a critical temperature slightly higher than is desirable for some low melt soaps but it can be employed with many anhydrous soaps such as lithium stearate, lithiumhydroxystearate and the like which have, a higher melting point. ,p

In extracting the grease it is desirable, although notv essential, to conduct the extraction under conditions which will cause the, least amount of disturbance of the soap structure. It has been found that the stability of the soap structure varies with different soaps. For example, the soap structure in lithium soap greases prepared in slab form is relatively stable and not readily disturbed or disrupted, whereas the soap structure of certain ,c'a'lcium soap greases generally prepared in "a workedform due to kettle'action during cooling is relatively easily disturbed or disrupted and becomes dispersed in the solvent. In cases wherein the soap becomes dispersed in the solv'entit is advisablealthough not absolutely essential, .to allow the soap to settle before proceeding with the solvent removal atgthe critical temperature; or such mixtures can be centrifuged prior to solvent removal. I M

It has been observed that greases have a definite fiber structure which varies according to the type of soap used and the 'preparation'of the grease. Thus, sodium greases have a definite fiber structure while greases. other than sodium also contain soap fibers, althoughin'some instances being Sosmall'that they'ca'nnot be resolved by an ultra m croscope but can be photographed after being suitably magnified by "an electron microscope. It is believed thatin the "extraction or leaching of the liquid vehicle from the'grea'se by means of a solvent, the vehicle is'removed from the fiber structure and replaced therein by a solvent. When the solvent is transformed'to a gas at the critical temperature there is no substantial change'in the structure of 'the's'oap'in the grease and as the gas is slowly removed the structure retains substantially the same shape as'it h'ad'in the initi 'al grease. While 'it is believed that the mechamsm by which 'this replacement or substitution of solvent "for-liquid vehi'cle takes I place is as taught in this theoretical discussion, it is to be understood that this theory is mere postulation which is oiiered for the purpose of explanation and not of limitation. A more thorou h theoretical discussion of the structure of greases can be found in a paper by G. V. Browning, A New Approach to Lubricating Grease Structure, delivered before the National Lubricating Grease Institute Convention at New Orleans, October 1949.

An application of the present invention is the preparation of silicone oil greases. Silicone oil greases cannot be readily prepared in the usual manner of merely heating together the soap and oil since a homogeneous mixture cannot be obtained in this manner. Instead two phases are invariably obtained with the silicone oil constituting one phase and the soap the other. This is particularly so in the case of lithium, calcium, aluminum and sodium fatty acid soap greases. However, by employing the herein-described invention, satisfactory homogeneous greases of silicone oil with lithium, calcium, sodium or aluminum fatty acid soaps can be obtained. Glycerin greases can also be prepared according to this invention but it is necessary, when introducing that polar vehicle into an expanded soap structure substantially free of liquid, to add a very small amount of polar solvent such as ethanol to the glycerin in order to permit the glycerin to be imbibed. It would appear that the glycerin, without the polar solvent, does not wet the soap structure and hence will not be drawn into the structure.

The following examples illustrate embodiments of this invention:

EXAMPLE I A lithium stearate lubricant grease comprising 12.5% soap by weight and a mineral oil having Saybolt Universal viscosity at 100 F. of 320 seconds was melted and cooled in the form of a slab. Blocks of grease measuring 2 x 2 x 1 centimeters were cut from this slab and the mineral oil was extracted therefrom. Whereas the oil can be extracted readily with propane it was found to be more convenient on a laboratory scale to remove the oil with hexane and then to extract the hexane with propane. The propane containing blocks of soap were then placed in a pressure bomb containing additional liquid propane. The temperature in the bomb was raised to 210 F. and 650 lbs, per square inch pressure, under which conditions the propane was permitted to escape slowly as a gas After all of the propane was emitted the bomb was opened and it was found that the blocks of soap had retained sub stantially the dimensions of the blocks of grease. The dimensions of the expanded soap were within 3% of the original grease. These blocks of soap had very low density and had a white, opaque appearance.

EXAMPLE I[ one of the blocks of expanded lithium stearate prepared according to Example I above was contacted at room temperature with a mineral oil having a Saybolt Universal viscosity at 100 F. of 320 seconds. The soap imbibed the oil to yield a grease which comprised 12.2% soap by volume as compared to 11.1% in the original grease from which the soap was derived. This difference may be due to the very slight shrinkage of the soap structure or to the occlusion of air. The reconstituted grease had an appearance and consistency similar to the original grease and had a micro-penetration of 54 compared to 58 for the original grease.

EXAlVUPLE DI One of the blocks of expanded lithium stearate prepared according to Example I above was contacted at room temperature with DC710 silicone polymer oil having a Saybolt Universal viscosity at F. of 1060 seconds. The soap imbibed the oil to yield a grease which comprised 12.2% soap by volume as compared to 11.1% in the original grease from which the soap was derived. The silicone grease thus prepared was very translucent and had a micropenetration of 62 as compared to 58 for the original grease.

EXAMPLE IV A block of the expanded lithium stearate prepared according to Example I above was contacted with glycerin in an efiort to prepare a grease but the soap would not imbibe the glycerin. The addition of a very small amount of ethanol resulted in the glycerin being drawn into the soap to produce a grease. It is believed that the ethanol enables the glycerin to wet the soap and thereby permit capillary action to proceed.

EXAMPLE V A lithium stearate lubricant grease comprising 7.3% soap by weight and a mineral oil having a Saybolt Universal viscosity at 100 F. of 360 seconds was melted and cooled in the form of a slab. Several one centimeter cubes were out from the slab and the oil was extracted with hexane. The hexane was evaporated at atmospheric pressure to give a collapsed soap structure which was only a small fraction of the size of the original block and had a relatively high density. All efforts to reconstitute a grease by imbibing the same or a different oleaginous liquid failed.

In order to determine the effect of working on the consistency of the reconstituted greases prepared according to Examples II and III above they were worked in a Hain micro-worker with 60 mesh screen and micropenetrations were measured with 10 strokes. The original grease of Example I was likewise worked in this manner. The results obtained are tabulated in the following table:

The herein-described invention which makes possible the removal of liquid vehicle from a grease composition and provides a method of introducing a second liquid vehicle provides a simple method of preparing greases which are otherwise difiicult to prepare, such as for example, the preparation of silicone polymer oil greases and greases in which a polar liquid such as glycerine is the liquid vehicle. Where it is desired to incorporate in the grease components other than. the oil and soap, such as for example, antioxidants, metal deactivators, pourpoint depressors, extreme pressure agents, solid lubricants, such as graphite, mica, etc., these may be added. after the second liquid vehicle has been imbibed.

which comprises selectively extracting the liquid vehicle from a lubricant grease, comprising essentially a mineral lubricating oil and lithium stearate of expanded structure, with liquefied propane, increasing the temperature of the propanecontaining soap structure to a temperature above about the critical temperature of propane but below the melting point of the soap while maintaining a pressure thereon sufiicient to maintain the propane substantially in the liquid phase at such increasing temperatures, slowly removing the propane from the soap structure at a temperature above about the critical temperature of propane but below the melting point of lithium stearate to obtain a substantially liquid free soap of expanded structure and introducing to the substantially liquid free soap structure glycerin containing in admixture therewith a small amount of a material capable of promoting the introduction of the glycerin to the expanded soap structure.

15. A method of removing the liquid vehicle from a lubricating grease, comprising a mineral lubricating oil and a soap of expanded structure, which method comprises selectively extracting the mineral lubricating oil from the soap with a liquid solvent having a critical temperature below the melting point of the soap, in which solvent the soap is substantially insoluble, placing the solvent-containing soap structure in a pressure vessel containing additional solvent, increasing the temperature of the solvent-containing soap structure to a temperature above about the critical temperature of the solvent but below the melting point of the soap while maintaining the solvent substantially liquid at such increasing temperatures and removing the solvent at a temperature between about the critical temperaure of the solvent and the melting point of the soap.

16. A method of obtainin a substantially liquid free soap of expanded structure from a lubricating grease, comprising essentially a normally liquid vehicle and a soap of expanded structure. which method comprising replacing said liquid vehicle in said soap structure with a liquefied normally gaseous solvent having a critical temperature below the melting point of the soap, in which solvent the liquid vehicle is substantially soluble and in which the soap is substantially insoluble, increasing the temperature of the solvent-containing soap structure to a temperature approximating the critical temperature of the solvent but below the melting point of the soap while maintaining a pressure thereon at least equal to the vapor pressure of the solvent at such increasing temperatures and removing the solvent from the point of the soap, in which solvent the soap is substantially insoluble, increasing the temperature of the solvent-containing soap structure to a temperature approximating the critical temperature of the solvent but below the melting point of the soap while maintaining a pressure thereon at least equal to the vapor pressure of the solvent at such increasing temperatures, removmg said solvent from said soap structure at a temperature between about the critical temperature of the solvent and the melting point of the soap and introducing to the expanded soap structure a normally liquid vehicle possessing lubrieating properties.

18. A method of obtaining a substantially liq- 1116. free soap of expanded structure from a lubricating grease. comprising essentially a normally l1quid vehicle and a soap of expanded structure, which method comprising displacing the liquid vehicle from the soap structure with a first normally liquid solvent, displacing the first normally liquid solvent with a second liquefied normally gaseous solvent having a critical temperature below the melting point of the soap, in either of which said solvents the liquid vehicle is substantially soluble and the soap is substantially insoluble, increasing the temperature of the second solvent containing soap structure to a temperature approximating the critical temperature of said second solvent but below the melting point of the soap while maintaining a pressure thereon at least equal to the vapor pressure of said second solvent at such increasing temperatures and removing the solvent from the soap structure at a temperature between about the critical temperature of said second solvent and the melting point of the said soap.

l9. A method of preparing a lubricant grease which comprises displacing the liquid vehicle from a lubricant grease, comprising essentially a normally liquid vehicle and a soap of expanded structure, with a first normally liquid solvent, displacing said first normally liquid solvent with a second liquefied normally gaseous solvent having a critical temperature below the melting point of the soap, in either of which said solvents the liquid vehicle is substantially soluble and the soap 1s substantially insoluble, increasing the temperature of the second solvent-containing soap structure to a temperature approximating the critical temperature of the second solvent but below the melting point of the soap while maintaining a pressure thereon at least equal to the vapor pres sure of said solvent at such increasin temperatures, removin said second solvent from said soap structure at a temperature between about the critical temperature of said second solvent and the melting point of the soap, and introducmg to the expanded soap structure a normally liquid vehicle possessing lubricating properties.

GEORGE V. BROWNING. GLENN M. WEBB.

No references cited. 

1. A METHOD OF OBTAINING A SUBSTANTIALLY LIQUIDFREE SOAP OF EXPANDED STRUCTURE FROM A LUBRICATING GREASE, COMPRISING ESSENTIALLY A NORMALLY LIQUID VEHICLE AND A SOAP OF EXPANDED STRUCTURE, WHICH METHOD COMPRISES DISPLACING THE LIQUID VEHICLE FROM THE SOAP STRUCTURE WITH A LIQUID SOLVENT HAVING A CRITICAL TEMPERATURE BELOW THE MELTING POINT OF THE SOAP, IN WHICH SOLVENT THE LIQUID VEHICLE IS SUBSTANTIALLY SOLUBLE AND IN WHICH THE SOAP IS SUBSTANTIALLY INSOLUBLE, INCREASING THE TEMPERATURE OF THE SOLVENT CONTAINING SOAP STRUCTURE OF THE SOLVENT-CONTAINING THE CRITICAL TEMPERATURE OF THE SOLVENT-CONTAINING LOW THE MELTING POINT OF THE SOAP WHILE MAINTAINING A PRESSURE THEREON AT LEAST EQUAL TO THE VAPORPRESSURE OF THE SOLVENT AT SUCH INCREASING TEMPERATURES AND REMOVING THE SOLVENT FROM THE SOAP STRUCTURE AT A TEMPERATURE BETWEEN ABOUT THE CRITICAL TEMPERATURE OF SAID SOLVENT AND THE MELTING POINT OF SAID SOAP. 